The 76 360 GP have as Mark said, have frame numbers starting at ML-6000 the engine number should start with 2055-xxxx, should have a olive (as in purple) tank, motoplat ignition small crankshaft end, gussets at the bottom of the frame main down tube as the 75 had some issues with the 75 frame cracking, different pipe, footpegs with square holes, different fork lowers and damper rods.
The 75 360 GP should have a maroon tank (brown colour), femsa points ignition large crankshaft end, different pipe as in two right angle bends coming out the header, (the 76 360 has a curved header from the outlet to the top straight section), the foot pegs were the older type with three raised holes.
There are not that many differences between them although the 76 is a bit mellower in the power band. The frame numbers for 75's start at ML-0000 and the engine number should be 2045-xxxx
In the GCRs 75 360GPs are not eligible for pre 75.
Is that Peter Worrall's old 360? His old number was 55.